Frequency-Variant Electronic Capacitor to Simultaneously Reduce Low-Frequency DC-Link Voltage Ripple and Improve Current THD of Grid-Connected Power Converters

Electronic capacitor (EC) is a circuit typically aimed to replace (in part or entirely) the bulk DC-link capacitor of a grid-interfacing power converter in a plug-and-play manner. EC is realized by a bidirectional dc-dc converter terminated with small auxiliary capacitor. The converter is controlled such that its DC-link side terminals mimic the behavior of a capacitor with much higher constant capacitance. In this article, a modification of the classical EC control structure is proposed, imposing the DC-link side terminals to emulate a frequency-variant capacitor rather than a constant one. The proposed algorithm allows achieving simultaneous reduction of both DC-link voltage ripple and grid-side current total harmonic distortion (THD) compared to ones attained by classical solutions, thus improving the tradeoff between DC-link voltage dynamics and ac-side current quality inevitably present in any grid-connected power converter. The proposed methodology is well supported by experiments.